This invention relates generally to a punch and die apparatus for removing a slug from sheet metal and the like, and more particularly to a male punch member for removing a non-round slug in at least two pieces from sheet metal, and the like. U.S. Pat. Nos. 4,543,722 and 4,353,164 are for draw punches which split a circular slug into two substantially equal parts during the process of forming a round hole in sheet metal. These patents and this application are commonly owned and the patents are incorporated herein in their entirety by reference.
In use, a punch and die are axially aligned with a sheet metal workpiece located therebetween. The punch and die are brought closer and closer together until the punch is recessed into the die cavity. In the process, the sheet metal is sheared by the cutting edges of the punch moving relative to a correspondingly shaped aperture of the die cavity. A disadvantage of these known draw punch constructions and operations is that prior to the development of the slug splitter punch, removal of the slug from the female die member was often difficult and time-consuming. Frequently, another tool such as a screw driver must be used to free the punched slugs. The above-cited patents eliminated this problem by splitting the slug along a diametral line into two semi-circular pieces, when forming circular holes in the workpiece.
Many openings to be formed in sheet metal are non-round. Square, oval, elongated rectangular and trapezoidal openings, for example, to receive connector sockets in computer housings, have become more common and punches have been developed to meet these applications. The slug removal problem is present also in these non-round opening applications. Accordingly, there is a need to develop apparatus for removing non-round slugs from their dies after forming with a punch, or to solve the problem by creating slugs which are per se more readily removable from the die, for example by producing a split slug as described above in connection with round hole punch and die sets.
The instantaneous force required to drive a punch through a sheet metal workpiece, for a given shaped opening, depends in some measure directly on the length of peripheral edge around the intended opening which is simultaneously being sheared. Thus, a flat die working face operates simultaneously around the entire periphery of the intended opening and requires considerable force. However, the punch travel is minimized.
Cutting edges which are set at an angle transverse to the direction of punch motion but not perpendicular thereto, reduce the required punching force by providing localized cutting rather than cutting around the entire periphery simultaneously. However, the reduction in force is accomplished with increased punch stroke. This force reducing technique is exemplified in the two above cited patents and in many other patents cited as prior art in those patent specifications.
As explained more fully hereinafter, the cutting edges in the U.S. Pat. No. 4,543,722, mentioned above, cause undesirable high force requirements when applied to non-round openings for punching with slug splitting. The desire to reduce required punch force in forming non-round openings requires that modification be made for some shapes in the tilt of the cutting surfaces relative to the direction of punch motion.
What is needed a non-circular slug splitter punch which is effective in reducing punch force requirements and provides a clean opening and a readily removable split slug.